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Cylinders: 3
Bore: 2.64 in.
Stroke: 2.68 in.
Displacement: 43.80 cu. in.
Aspiration: Natural

Length: 26.40 in.
Width: 18.80 in.
Height: 20.10 in.
Weight: 241.00 lbs.

Introducing the Universal B-Series - The Legend Continues

Makers of the world famous Atomic-4 and pioneers in premium marine diesel propulsion, Universal has struck again with its latest release, the Universal B-Series. The B-Series is powered by the latest advancements in diesel engine design. Some of the benefits from these advancements include cleaner emissions, reduced noise levels, and increased horsepower at lower RPMs. All B-Series engines are naturally aspirated and deliver high low-end torque. This produces some of the most quiet and durable marine engines currently available.

If you’re looking to replace that aging Atomic-4, the Universal B-Seriesis still the boaters choice for Atomic-4 replacements**. The M-25XPB and M3-20B offer many similar dimensional characteristics to the Atomic-4, making for a much easier installation.

Universal holds a large inventory of spare parts for your engine including easy-to-buy spare parts kits and gasket sets tailored to your particular engine. It’s easy to see why Universal is as popular today as it was 100 years ago. Stop by your local Universal Distributor or Dealer today to learn more about the latest in Universal Marine Power.

**Universal Atomic-4 replacements are not direct drop-ins in all cases.
Some engine compartment reconfiguration may be required.

Standard Equipment

  • Fresh water cooling
  • Engine prewired to plug-in connector
  • E-Z bleed fuel system
  • 12 volt, 51 ampere alternator
  • Coolant recovery tank
  • Domestic hot water connection
  • Throttle and shift control brackets
  • Low oil pressure and high water temperature alarms
  • Gear-driven sea water pump
  • Transmission with 2.05:1 reduction
  • Glow plug cold starting aid
  • Engine matched four point adjustable mounts - fail safe neoprene
  • Mounting centers - 11.5", 16.0"
  • Lube oil drain hose
  • Oil fill - Top
  • Circuit breaker protected electrical system
  • Operator’s Manual and Parts List


Optional Equipment

  • Captain panel with alarm (tachometer with lights)
  • Admiral panel with alarms (tachometer with gauges)
  • Dual station senders
  • Other gear ratios - Consult local Distributor
  • Hydraulic transmissions - Consult local Distributor
  • Remote expansion tank
  • Muffler and fittings
  • "A" and "B" on board spare parts kit
  • Alternator, 72 amp single output
  • Anti-siphon valve for overboard cooling discharge water
  • Technical Manual
  • Exhaust connection - 45 and 90 degree elbows, exhaust riser
  • Propeller shaft couplings 






Technical Documents

Important Note: Technical information is provided on our website for your reference and convenience. Westerbeke recommends that your engine, generator or climate control system is serviced and/or installed only by an authorized Westerbeke distributor or dealer. Click here to locate the Master Distributor or Dealer for your area.

Advanced Specifications
Document Name Publication Date
  Advanced Specifications 7/1/2015
Manuals (Operators, Parts, Technical, Installation)
Document Name Publication Date
  Installation Manual - Marine Engines & Generators 6/1/2016
  Operator's Manual 200550 8/1/2015
  Universal Superseded Parts Listing August 2015 8/1/2015
  Parts Manual 201009 6/1/2001
  Technical Manual 200562 N/A
Guides (Troubleshooting)
No matching records found
Diagnostic Software
No matching records found
Diagrams (Wiring, Installation)
Document Name Publication Date
  039144 Revision M 3/2/2009
  Wiring Diagram 039144 Revision J 12/12/2008
  Wiring Diagram 039144 Revision K 12/12/2008
  Wiring Diagram 039144 Revision L 12/12/2008
  Wiring Diagram 039144 Revision N 8/7/2008
  Installation Drawing 201088 N/A
Bulletins (Service, Parts, Product Recalls)
Document Name Publication Date
  Parts Bulletin 2007-1: Part Number Errors M3-20B

Applies To:

  Service Bulletin #242: Manufacture Date Code

  Service Bulletin #236: Universal Propulsion R.P.M. Ranges

  Service Bulletin #238: Fuel Pump Inlet Filter Part Number 048076

  Service Bulletin #155: Keyswitch

  Service Bulletin #136: Shift Lever

  Service Bulletin #125: Oil Pressure Switches





Buy and View Parts Below : Click each image for a larger view and detailed list of the parts for that section. If images do not appear under a "Complete Parts Lists" heading, please scroll down to access the parts related information available for this model.


Download Parts Documentation
Document Name Publication Date
  Parts Manual 201009 6/1/2001
Superseded Parts List
Document Name Publication Date
  Universal Superseded Parts Listing August 2015 8/1/2015